1. Field of the Invention
The present invention relates to a system and a method for conducting secret communication through a preexisting digital communication channel (network).
2. Description of the Related Art
Privacy and encrypted communications over the Internet are gaining more and more prominence. Some governments (Great Britain and Russia are current examples) either forbid private citizens from using encryption or require that the keys to the encrypted messages be handed on demand to government agencies.
Steganography is the practice of disguising the existence of a particular message. In modern usage, this generally implies that some information of interest (auxiliary data) will be hidden in, what is known to those skilled in the art, as cover data. Commonly used cover data includes images, audio files and e-mail. Although the term “steganography” is most often used to describe the class of schemes by which auxiliary data is hidden in cover data, it has a broader connotation by which it also envelopes systems which enable secret communication to take place.
When secret communication between two or more individuals occurs, there is inevitably an encryption which takes place. This encryption can be as simple as an agreed upon hand signal for secret communication in public, or as complex as the most sophisticated digital steganographic techniques. However, no system of encryption is unbreakable, and once detected it can compromise not only the particular message that was detected, but the identities of the parties involved in the secret communication. As personal privacy on the Internet and in digital communication continues to be challenged, there is a need in the art to provide an improved system and method of secret communication in a digital network.
1Several broad-based disclosures, i.e., “Digital Steganography” by Donovan Artz and “Invisible Communication” by Tuomas Aura have addressed aspects the field of steganography. These treatises cover the field in general terms and have no impact on the novelty and non-obviousness of the present invention.
For example, the “Digital Steganography” article by Artz is a survey of commonly used data hiding techniques. It mentions in general terms that unused header segments of a data file would seem to be excellent places to hide data. Thus, based upon this disclosure, the skilled artisan would deduce techniques for hiding data in data header structures, such as comment fields and unused segments. Artz also discloses a number of techniques which involve hiding data in structures by permuting particular table entries or header segments using a predetermined mapping of the possible permutations to a pre established code alphabet.
Artz seems to imply the concept of “trickling” the data out in small pieces into a high-volume stream of cover data sets in an attempt to avoid the suspicion that a large amount of hidden data in a single cover set might cause.
The article by Aura also discusses using the header of a data file as the carrier of hiding data.
Another disclosure relating to this field is entitled “A Scheme of Secret Communication Using Internet Control Message Protocol” by Masataka Suzuki and Tsutomu Matsumoto, found in IEICE Trans. Fundamentals, Vol. E85A, No. 1, January 2002. This article details a method by which an existing network can be used to conduct secret communication by forcing errors into network traffic in such a way that the returned error message effectively contains the secret communication.
The Suzuki/Matsumoto method noted above is substantially different from the very special scheme of interception embodied in the present invention which allows for normal, error-free operations to continue while secret communication goes on. Contrary to the method disclosed above, by which an existing network can be used to conduct secret communication by forcing errors into network traffic in such a way that the returned error message effectively contains the secret communication, the present invention, as is explained in greater detail hereinafter, utilizes direct interception of network traffic as a main communication method which can be augmented by additional steganographic techniques, for example a Huffman table hiding method.
It is hereby emphasized the method of the present invention explicitly involves exploitation of “unused” Huffman codes in any way deemed appropriate. There is no explicit mention in any of the prior art articles cited above of any structure remotely similar to unused Huffman codes.